In adult goldfish, the regenerative growth of severed optic axons back to the optic tectum will be used as a model system for the normal development of selective axon connections. In following leads developed from our previous work, retina, tectum or optic pathways are to be variously altered surgically, and the response of regenerating fibers and the resulting retinotectal projection systematically measured. The methods include an eye-in-water electrophysiological recording technique for accurately mapping the terminal arborizations of optic fibers and various anatomical procedures in particular autoradiography and HRP backfilling. These methods will be applied toward further analysis of the following: (1) the inhomogeneities and asymmetries in the reorganized retinotectal projection which follows various retinal and tectal ablations, (2) the segregation of fibers which have been surgically deflected into the wrong, ispsilateral tectum from the optic fibers which normally innervate this tectum, (3) the disorderly projection that results when only a small number of fibers are permitted to innervate the tectum and (4) aberrations in the pathways taken by regenerating fibers. In addition, thymidine labelling and autoradiography as well as cell counting will be aimed at further study of (5) the continual addition of new cells to the retina and tectum of normal juvenile and adult goldfish.